I would go berserk (and also try to use the electricity I presumably have to watch said shows for a more practical purpose, but here goes...
  1. Buffy the Vampire Slayer
    Because it's my favorite and I would never get bored of it.
  2. M*A*S*H
    Because 11 seasons of the best witty writing ever.
  3. Whose Line Is It Anyway
    Because it never fails to make me laugh, and despite its fleeting, one-time-only nature, it has quite the rewatch value. Note I'm not differentiating between the UK, US, and US reboot versions.